1. Field of the Invention
The present invention relates to mounting structures for mounting power elements to a heat dissipation member, and more particularly to the mounting structures of a type that is suitable for a brushless motor.
2. Description of the Prior Art
As is known, a power element is a control element that controls voltage and/or current and generates a certain heat under operation. For effectively removing such heat, various mounting structures have been proposed and put into practical use. One of them is disclosed in Laid-open Japanese Patent Application 2000-32729, whose essential portion is shown in FIG. 20 of the accompanying drawings. In this mounting structure, heat generated from the power element is transferred to a heat dissipation member through a heat sink. In the drawing, denoted by numeral 105 is a power element. The power element 105 contacts to a leg portion 107 of a heat sink 101. The heat sink 101 is formed with a plurality of heat dissipation fins 103 which serve as the heat dissipation member. Terminals 109 of the power element 105 are soldered to a circuit on a circuit board 111. The leg portion 107 of the heat sink 101 is connected to the circuit board 111 by means of a bolt 113. As shown, the power element 105 is pressed against a surface 115 of the leg portion 107 by means of a spring member 117. Thus, under operation, heat generated from the power element 105 is transferred to the heat dissipation fins 103 through the leg portion 107.
However, in this conventional power element mounting structure, provision of the leg portion 107 causes increase in length of a so-called heat travelling path and thus makes the heat dissipation effect poor. Furthermore, in this mounting structure, the leg portion 107 needs a certain strength and thus a larger size because it has to hold the power element 105 and has to serve as a good heat transferring means. Of course, in this case, the power element mounting structure becomes bulky, heavy and costly.
It is therefore an object of the present invention to provide a structure for mounting power elements to a heat dissipation member, which is free of the above-mentioned drawbacks.
According to the present invention, there is provided a structure which comprises a circuit board; a spring plate of metal, the spring plate being resiliently mounted, through a first mounting structure, on the circuit board keeping a given space therebetween; a plurality of power elements disposed on the spring plate to form a semi-assembled unit; a heat dissipation member of metal having a plurality of heat dissipation fins on an outer surface thereof, the heat dissipation member being mounted, through a second mounting structure, on the semi-assembled unit in such a manner that an inner surface thereof faces toward the power elements; and a plurality of spring pieces defined by the spring plate, the spring pieces being arranged to press the power elements against the inner surface of the heat dissipation member.